Effects of cooling rate on the microstructure and tensile behavior of a Sn-3.5wt.%Ag solder

Abstract

The tensile behavior and microstructure of bulk, Sn-3.5Ag solders as a function of cooling rate were studied. Cooling rate is an important processing parameter that affects the microstructure of the solder and, therefore, significantly influences mechanical behavior. Controlled cooling rates were obtained by cooling specimens in different media: water, air, and furnace. Cooling rate significantly affected secondary dendrite-arm size and spacing of the Sn-rich phase, as well as the aspect ratio of Ag 3 Sn. The Sn-rich dendrite-arm size and spacing were smaller for water-cooled specimens than for air-cooled specimens. Furnace cooling yielded a nearly eutectic microstructure because the cooling rate approached equilibrium cooling. The morphology of Ag 3 Sn also changed from spherical, at a fast cooling rate, to a needlelike morphology for slower cooling. The changes in the microstructure induced by the cooling rate significantly affected the mechanical behavior of the solder. Yield strength was found to increase with increasing cooling rate, although ultimate tensile strength and strain-to-failure seemed unaffected by cooling rate. Cooling rate did not seem to affect Young's modulus, although a clear correlation between modulus and porosity was obtained. The mechanical behavior was correlated with the observed microstructure, and fractographic analysis was employed to elucidate the underlying damage mechanisms.

Effect of Bismuth and Silver on the Corrosion Behavior of Lead-free Solders in 3.5 wt% NaCl Solution

“…It is known that the bismuth additions can significantly depressed the melting temperature of Sn-Ag-based lead-free solder alloys [13,14]. Further advantage of adding bismuth into Sn-Ag system solder is the improvement of solder wetting/spreading behaviour [15,16]. It was also already shown that bismuth and silver can have a significant impact on the corrosion properties in case of Sn-based solder alloy in NaCl solutions [17,18].…”

Isothermal Fatigue Properties of Sn–Ag–Cu Alloy Evaluated by Micro Size Specimen

“…Therefore, a number of studies on mechanical fatigue of solder alloys to understand fatigue failure of solder joints have been performed to date. In general, mechanical properties of solder alloys such as creep and fatigue are measured using larger volume bulk specimens than real solder joints [1][2][3][4][5] as there are many difficulties in sample preparation and mechanical testing. However, the microstructure of the real joint is totally different to that of the large size mechanical testing specimen, since solidification conditions of real joints cannot be duplicated in large size.…”

The effect of CuSn intermetallics on the interstrand contact resistance in superconducting cables for the large hadron collider

“…For Sn-3.5Ag/Cu couples at 170 °C and at 205 °C a t 0.42 time dependence has been found for the Cu 3 Sn growth [15]. The kinetics for the intermetallic formation and the intermetallic microstructure depend for instance on the cooling rate [16] and the presence of other elements in the coating bath, such as Cu [17], which is dissolved in the coating bath from the strand during the coating process.…”